Hydrogen (high-purity hydrogen) is utilized in various industrial fields such as metal heat treatment, glass melting, semiconductor -manufacturing or optical fiber manufacturing. Hydrogen is also used as the fuel of a fuel cell.
An example of hydrogen production system for industrially producing hydrogen is disclosed in Patent Document 1 given below. The hydrogen production system disclosed in Patent Document 1 includes a gasifier, a reformer, a gas-liquid separator and a pressure swing adsorption gas separation apparatus and is designed to produce hydrogen using a hydrocarbon-based material as the main material. The gasifier serves to heat and gasify a mixed material containing a hydrocarbon-based material such as methanol or natural gas, water and oxygen before it is supplied to the reformer. In the gasifier, the mixed material flowing in the gasifier is heated to an appropriate temperature by utilizing high-temperature combustion gas produced by burning fuel as the heat source. In the reformer, the gasified mixed material is subjected to reforming reaction to obtain reformed gas (containing hydrogen). Specifically, in the reformer, both of steam reforming reaction which is endothermic reaction and partial oxidation reforming reaction which is exothermic reaction occur. For instance, in the steam reforming reaction, hydrogen as the main product and carbon dioxide as the sub product are produced from methanol and water. For instance, in the partial oxidation reforming reaction, hydrogen as the main product and carbon dioxide as the sub product are obtained from methanol and oxygen. In the gas-liquid separator, before the reformed gas produced by the reformer is supplied to the pressure swing adsorption gas separation apparatus which will be described later, the liquid component contained in the reformed gas is separated and removed from the gas and discharged as drain. In this hydrogen production system, the composition of the mixed material is so adjusted that the amount of heat absorbed by the steam reforming reaction and the amount of heat generated by the partial oxidation reforming reaction balance each other, whereby autothermal reforming reaction proceeds in which the reaction temperature in the reformer is maintained substantially constant.
Patent Document 1: WO2006/006479
The pressure swing adsorption gas separation apparatus serves to adsorb and remove unnecessary components, i.e., components other than hydrogen from the reformed gas to produce hydrogen-rich gas as product gas. The apparatus includes at least one adsorption tower loaded with an adsorbent for adsorbing preferentially the unnecessary components contained in the reformed gas. In the pressure swing adsorption gas separation apparatus, gas separation by the pressure swing adsorption gas separation method (PSA separation method) is performed. For instance, in the gas separation by the PSA separation method, a cycle including an adsorption step, a desorption step and a regeneration step is repetitively performed in an adsorption tower. In the adsorption step, reformed gas after passing through the gas-liquid separator is supplied into the adsorption tower where the unnecessary component contained in the reformed gas is adsorbed under high pressure, whereby hydrogen-rich gas is discharged from the adsorption tower. In the desorption step, the pressure in the adsorption tower is reduced for desorbing the unnecessary component from the adsorbent, and the gas (offgas) containing hydrogen remaining in the tower and the unnecessary component is discharged from the adsorption tower. In the regeneration step, the adsorption ability of the adsorbent for the unnecessary component is recovered by e.g. supplying cleaning gas into the adsorption tower.
In the adsorption step described above, the reformed gas from which the liquid components have been removed by passing through the gas-liquid separator is introduced Into the adsorption tower. Thus, the liquid components in the reformed gas are prevented from entering the adsorption tower. As a result, the deterioration of the adsorbent in the adsorption tower due to the contact with liquid components is prevented.
The offgas discharged from the adsorption tower is supplied to the gasifier as the fuel for combustion (fuel for gasifying the mixed material). In the gasifier, hydrogen gas contained in the offgas is burned to produce high-temperature combustion gas. The mixed material flowing within the gasifier is heated by the combustion gas utilized as a heat source to be gasified. The combustion gas after used for heating the mixed material in this way is discharged into the atmosphere.
In the hydrogen production system disclosed in Patent Document 1, the amount of offgas to be discharged from the PSA separation apparatus and supplied to the gasifier (supply per unit time) in the operation can be adjusted. This adjustment ensures that, during the normal operation after the lapse of a predetermined time from the start of the operation, the fuel required for heating and gasifying the mixed material at a desired temperature in the gasifier is provided only by the offgas supplied from the PSA separation apparatus. Moreover, in the hydrogen production system disclosed in Patent Document 1, the interior of the reformer is maintained at a desired reaction temperature by adjusting the ratio between the steam reforming reaction and the partial oxidation reforming reaction of the hydrocarbon-based material proceeding in the reformer. In this way, in the normal operation of the hydrogen production system disclosed in Patent Document 1, the heating and gasifying of the mixed material is performed only by the self-generating heat obtained in operating the system, and the interior of the reformer is maintained at a desired temperature. With such a thermally-independent hydrogen production system, hydrogen is produced efficiently by avoiding the inefficient technique of continuously heating the mixed material and the interior of the reformer by burning external fuel.
In recent years, restrictions on environmental pollutant and hazardous substances are strict, and further, restrictions on a method for treating industrial waste also tend to become strict. In the hydrogen production system disclosed in Patent Document 1, the drain removed by the gas-liquid separator is mainly composed of water contained in the mixed material. When the hydrocarbon-based material constituting the mixed material is methanol, the drain may contain unreacted methanol. In this case, to comply with the recent restrictions on hazardous substances, it is necessary to additionally provide a facility exclusively used for drain treatment or provide a facility for storing the drain and transfer the stored drain to a dealer as industrial waste.
However, to additionally provide a facility for drain treatment is not desirable, because the installation of the facility requires high cost. On the other hand, when the drain is to be disposed of by utilizing a drain storage facility, the cost for the maintenance and disposal of the drain is necessary in addition to the cost for installing the storage facility. Such cost for maintenance and disposal increases in accordance with an increase in the amount of drain, which increases in direct proportion to an increase in the amount of product gas (hydrogen-rich gas). These problems about the drain treatment are not peculiar to this hydrogen production system. For instance, other equipment or apparatuses for producing gas may involve the same problems.